I ran a highflow last year and it made a difference. I will be looking to get the Stromong catless track pipe for track days.
The highflow helped out a bunch and probably more with no cats but I only recommend it for the track as like tapper said, it's will make you car much louder. I ended up run a quicker 1/4 mile with the high flow. I got down to a 15.1
I would bet with no cats it would go quicker. Just keep your exhaust at about 2 1/4".
My engine mods when I ran a 15.1 were custom intake, Borla header, UDP, highflow cat and custom 2 1/4" catback.
I do want to see about getting a reprogramed stock ECU for a higher redline and maybe some help in the power department. I am back with my stock cats as I am back running Solo2 STS class.
You will need to invest in a CEL fix as some highflow cats will give you CELs.